Expansion joints for use in coupling spaced apart sections of duct systems for fluid media, whether the ducts are square or circular in cross section, have structural connections with the proximate ends of such sections and a sleeve of flexible material sealed to the connections with the purpose of surrounding and isolating the flow path in the area between the section. The sleeve materials have at least one reinforcing woven substrate to which elastomeric surface layers are bonded.
In an installed expansion joint, the material is normally bowed to accommodate expansion and contraction forces, inwardly when a subatmospheric pressure prevails in a duct system and outwardly when the duct pressures are positive.
The problem that exists with presently used sleeves is that the strands of whatever materials are used to form the substrate or substrates are incapable of responding to the demands for their extension or reduction which are attended by the outward and inward transverse bowing associated with varying duct temperatures and pressures. As a consequence, the integrity of the sleeves is often adversely affected by the compound wrinkles and bends which develop in service with rupturing of the bonds between the substrates and the elastomeric layers being one result and the cutting of the layers when the substrates are wires being another. Wire substrates of the knitted type incorporating a loop profile have the objection that the wire loops are required to straighten beyond their elastic limits when subjected to such perimetric changes typically required.